Polyalkenyl substituted olefinic mono- and dicarboxylic acid or anhydride producing materials, most notably polyisobutenyl succinic acids and anhydrides, are known intermediates for the preparation of products useful as additives in lubricants, fuels, and functional fluids. In particular, polyalkenyl succinic anhydrides have been used as emulsifiers and compatibilizers, and succinamide and succinimide products produced by the reaction of monoamines or polyamines with polyalkenyl succinic anhydrides have been employed as ashless dispersants and detergent additives in lubricating oils and in fuels.
Polyalkenyl substituted olefinic mono- and dicarboxylic acid and anhydride producing materials have been prepared using a one-step halogen-assisted reaction process in which a polyalkene and an unsaturated olefinic mono- or dicarboxylic acid or anhydride producing compound (hereinafter referred to for the sake of convenience as “CAP compound(s)”) are reacted at elevated temperature in the presence of chlorine. Such polyalkenyl dicarboxylic acid materials have also been prepared using a two-step halogen-assisted process in which the polyalkene is chlorinated in the first step and the resulting chlorinated polyalkene is then reacted with the CAP at elevated temperature. Both the one- and two-step chloro processes can produce polyalkenyl substituted dicarboxylic acid materials in relatively high yields. However, these products typically contain residual chlorine, and environmental concerns related to chlorine-containing materials make the use of the chloro processes undesirable.
The polyalkenyl substituted carboxylic materials have also been prepared by the direct thermal reaction of a polyalkene and CAP compound, often referred to in the art as the thermal (or “ene”) process. While the thermal process has the advantage of avoiding the use of chlorine, the reaction tends to proceed only slowly and with low yields at reaction temperatures below about 150° C. At higher reaction temperatures, e.g., temperatures above 180° C., the yield of the thermal process improves.
Improved thermal process yields have been achieved using polyalkene reactants having a relatively high proportion of terminal double. Terminal double bonds, particularly terminal vinylidene bonds, in polyalkenes are recognized to be generally more reactive in the thermal process than internal double bonds. U.S. Pat. No. 4,152,499, for example, discloses that adduct formation between maleic anhydride and polyisobutene occurs virtually only between maleic anhydride and a terminal double bond. U.S. Pat. No. 4,152,499 further discloses that double bonds in the β position are also capable of reacting to a certain degree, while virtually no reaction occurs at double bonds further removed from the chain ends. U.S. Pat. No. 4,086,251 discloses that terminal vinylidene is believed to be the most reactive of the terminal double bonds in polybutenes. Conventional polyisobutenes, formed by cationic polymerization using aluminum chloride catalysts such as AlCl3, generally have a relatively low content of terminal double bonds. Polyisobutenes having a high content of terminal double bonds, so-called “reactive” polyisobutenes, have been achieved by BF3-catalyzed polymerization of isobutene. Other polyalkenes having a high content of terminal double bonds (e.g., ethylene-α-olefin copolymers and α-olefin homo- and copolymers) prepared by polymerization of the corresponding monomers in the presence of metallocene catalyst systems have also been disclosed.
Both the halogen-assisted and thermal reactions described above also tend to produce significant amounts of a sediment byproduct which must be filtered from the final product prior to the use thereof as an additive or intermediate. The thermal process also tend to produce tars that coat the reactor walls, necessitating frequent, time-consuming, and costly clean-ups of the reactor vessel. Sediments are believed to be due at least in part to the decomposition and/or self-polymerization of the CAP compound. Tar formation is believed to be due to the self-polymerization of the CAP compound, which is typically maleic anhydride.
In association with the practice of the thermal reaction, it is known that the use of a reactive polyalkene improves yield and reduces tar formation relative to a “conventional” polyalkene. Further, the use of certain process steps and the addition of certain additives are known to further reduce the formation of both tar and sediment. For example, U.S. Pat. No. 4,235,786 discloses that tar and sediment formation in such a thermal reaction can be reduced by conducting the reaction in the presence of an oil-soluble strong organic acid. U.S. Pat. No. 5,777,025 describes a process in which a thermal reaction is conducted at elevated temperature and pressure in the presence of a sediment-inhibiting amount of an oil soluble hydrocarbyl-substituted sulfonic acid. U.S. Pat. No. 4,472,588 describes a thermal reaction between a polyalkene and maleic anhydride, in which the maleic anhydride is added incrementally such that a single homogeneous phase is maintained in the reactor. The patent notes that such a process results in the formation of a reduced amount of resin (tar).
Reactor fouling by self-polymerized CAP compound reduces the rate of heat transfer between the reactor heating medium and the reactor contents. This results in prolonged cycle times and therefore, reduces plant capacity. Also the process by which the CAP compound self polymerize is auto-catalytic. Therefore, minimizing the presence of tar reduces the rate at which additional tar is formed. In extreme cases where reactor fouling leads to the formation of significant deposits, mechanical damage to mixing equipment and/or blockage of drain valves can result. While the use in a thermal reaction of reactive polymer has been found to reduce tar and sediment formation, and certain process steps and additives are known to further ameliorate both tar and sediment formation, it would be advantageous to find improved thermal processes that further reduce the amount, or completely eliminate sediment and/or tar, most particularly tar, such that the repetitive cleaning of the reactor becomes unnecessary. More specifically, while known processes may reduce the amount of tar formed, even minimal amounts of tar can build up on the reactor walls over time, fouling the reactor. Therefore, there remains a need for a process for thermally reacting polyalkene and CAP compound, which process is capable of both reducing the amount of tar formed in any single batch reaction, and removing from the reactor walls residual tar deposited on the reactor walls during prior reactions.